Mesophase dope containing cellulose derivative and inorganic acid

ABSTRACT

A mesophase dope useful for producing shaped articles, for example, filaments and films, comprises at least 10% by weight of at least one cellulose derivative and the balance consisting of an aqueous solution of at least 5% by weight of at least one inorganic acid, the dope exhibiting the mesophase property even in the case where no fluid dynamic stress is applied thereto.

This is a division of application Ser. No. 188,854, filed Sept. 19, 1980now U.S. Pat. No. 4,370,168.

FIELD OF THE INVENTION

The present invention relates to a mesophase dope. More particularly,the present invention relates to a mesophase dope comprising a cellulosederivative material dissolved in an aqueous solution of an inorganicacid material, the viscosity of which dope is capable of being adjustedto a value suitable for forming the dope into filaments or a film whilemaintaining the mesophase property of the dope.

BACKGROUND OF THE INVENTION

The term "mesophase dope" used herein is defined by F. C. Frank,Discussin Faraday Society, 25, 19(1958), as follows. That is, the term"mesophase dope" refers to a dope, which exhibits such a property thatthe movement of the centers of gravity of the molecules, from which thedope is formed, is carried out fluidly, and the change in orientation ofthe molecules is carried out elastically. The mesophase dope of thepresent invention should be distinguished from a dope having such aproperty that, when the dope is placed in a fluid dynamic field, forexample, when a fluid dynamic force is applied to the dope so as tocreate a velocity gradient of the dope and, therefore, to produce ashearing force on the dope, a fluid birefringence is created in thedope. In other words, the mesophase dope of the present invention is adope exhibiting a bright interference color visible to the naked eye dueto a certain type of systematic arangement or orientation of themolecules from which the dope is formed, even in the core where nostimulation is applied from the outside to the dope. In still otherwords, the mesophase dope of the present invention is a dope exhibitingliquid and solid properties that the dope exhibits a bright field ofview under an orthogonal Nicol's prism of a polarizing microscope. Inthis regard, the term "mesophase dope" has the same meaning as the terms"liquid crystal", "optical anisotropic liquid" and "ordered liquid". Inthe present invention, the mesophase dope is a liquid crystal created byan interaction between a polymer and a certain solvent. Therefore, whenthe mesophase dope of the present invention is subjected to a wetspinning process, the resultant filaments have a high degree oforientation of the polymer molecules therein without applying a drawingprocedure as in the case of ordinary spun filaments.

It is known that solutions or melts of various polymers having rigidmolecular chains, for example, synthetic polypeptides, aromaticpolyamides, aromatic polyamidehydrazides, aromatic polyazomethines andaromatic polyesters, form mesophase dopes. Flory (Proceedings of theRoyal Society, Series A 234,73(1956)) conducted research on astatistical treatment of rigid polymer dope and provided a generalexplasion of the free energy in mixing of rigid polymers, as a functionof the mole number of the rigid polymer, axial ratio and disorientationcoefficient of solute molecule. Also, Flory predicted a separation of anoptical anisotropic phase from isotropic phase of the rigid polymer at acritical concentration of the rigid polymer dope. The phase separationis derived from asymmetry of the particles in the dope. That is, in thedope of the rigid polymer, the concentration of the anisotropic phaseremarkably increased due to the relatively small positive interactionenergy.

In a dope of a semi-flexible polymer the molecules of which have acertain flexibility, the mesophase property of the dope depends mainlyupon the length of a rigid segment in the semi-flexible molecule.

Accordingly, it is practically and theoretically supported that aspecific solution of a rigid polymer or semi-flexible polymer can form amesophase dope.

Since Flory et al studied the polymer dopes, various discussions havebeen made on the flexibility of molecular chains of various cellulosederivatives. However, the discussions were not correct, because thedraining effect of solvent was not properly considered in thediscussions.

Recently, Kamide et al (Polymer Journal, 10, 4,409(1978)) carefullyanalyzed data concerning the properties of solutions of variouscellulose derivatives and reached a conclusion concerning theflexibility of the molecular chains in the cellulose derivatives.Concerning the conclusion, it should be noted that the expanse of themolecular chain of the cellulose derivative, and the rigidity of themolecular chain in an unperturbation state are remarkably variabledepending on the type of solvent used, and the rigidity of the molecularchain of the cellulose derivative is definitely higher than that ofvinyl polymers. The above-mentioned properties of the cellulosederivative are derived from the polar hydroxy (-OH) groups in itsmolecule and the hetero-oxygen atom located between molecules, andtherefore, are variable depending upon the degree of substitution of thecellulose molecule.

Japanese patent application Laid-open (kokai) No. 52-96230 discloses thefact that an optical anisotropic dope is obtained from a combination ofa cellulose derivative having a degree of substitution of 1.0 or morewith a specific solvent. From the teaching of the cellulose chemistry,it is known that an increase in the degree of substitution of hydrogenatoms in the hydroxy groups in cellulose molecules by substituents,especially, hydrophobic substituents, for example, alkyl or estergroups, causes the solubility of the resultant cellulose derivative inan organic solvent to be increased. However, generally, it is difficultto obtain a uniform solution by dissolving the cellulose derivative inan organic solvent, because of formation of partial gel in the solution.In the case of a mesophase dope in which a cellulose derivative has tobe dissolved in a very high concentration of 15% by weight, or more inthe organic solvent, the formation of the partial gel is promoted.Therefore, in this case, it is very difficult to obtain a uniformstructure of mesophase dope of the cellulose derivative. Also, thenon-uniform dope can not be convented into a shaped article having auniform quality. Furthermore, it is very difficult to completelyeliminate the organic solvent from the resultant shaped article. Thislast difficulty causes a problem in the quality of the resultant shapedarticle.

The above-mentioned Japanese laid-open specification disclose severalinorganic solvents for forming the mesophase dope of the cellulosederivative, however, the aqueous solution of inorganic solvent is notdescribed as a solvent for the mesophase dope in the early publication.For example, combinations of hydroxypropylcellulose (HPC) with water, asodium salt of carboxymethylcellulose (CMC-Na) with water, CMC-Na withan aqueous solution of sodium hydroxide, CMC-Na with an aqueous solutionof sodium chloride and a sodium salt of cellulose sulfate with water,are described in the laid-open specification. However, in order to formthe mesophase dopes from the above-mentioned combinations, it isnecessary that the almost all of the cellulose derivatives be used in ahigh concentration of 50% by dry weight or more. Such high concentrationof the mesophase dope is not suitable for producing shaped articlestherefrom. Even in the case where a mesophase dope can be produced fromabout 30% by dry weight of the cellulose derivative and the inorganicsolvent, the resultant mesophase dope is in the state of a paste andexhibits a poor filament-forming property. Also, the use of theabove-mentioned salt solution or alkali solution causes such a problemthat metal element from the inorganic solvent is retained in theresultant shaped material or that the waste water from the shapingprocess has to be clarified so as to avoid public polution of rivers,the sea or lakes.

On the other hand, various inorganic acids which are not described as asolvent for the cellulose derivative in above-mentioned Japaneselaid-open specification, are utilized for depolymerizing cellulosematerials so as to produce pulp having a desired degree ofpolymerization. However, due to their high depolymerizing effect, theinorganic acids have not been used as a solvent for the cellulosederivative. For example, in the preparation of cellulose acetate orcellulose nitrate, it has often been experienced in the celluloseindustry that the cellulose material is remarkably depolymerized byinorganic acid, such as sulfuric acid, and the resultant productcontains a certain amount of the SO₄ ²⁻ ion, which results inundesirable formation of gels in the solution of the cellulosederivative. From the above-mentioned experience, the use of theinorganic acid has been avoided by the cellulose industry.

Also, E. Otto and Spurline's edited Cellulose, Parts I to III, andCellulose and Cellulose derivatives, Parts IV and V, Inter Science, inwhich cellulose chemistry is described in detail, contains substantiallyno description concerning the solubility of the cellulose derivatives inthe inorganic acids, whereas the solubility of the cellulose derivativesin water or various alkali solutions or organic solvents is describedvery much in detail therein.

The inventors of the present invention conducted detailed studiesregarding the expanse and, in its turn, the rigidity of the molecularchains of the cellulose derivatives in various solvents, in accordancewith the theorem that the expanse of the molecular chains of a polarpolymer in unperturbation state is promoted in a polar solvent. Also,while considering the disadvantages of the organic solvents andinorganic salt aqueous solution used as a solvent for the cellulosederivatives, the inventors of the present invention studied theproduction of a mesophase dope from cellulose or cellulose derivatives,for example, cellulose ethers or cellulose esters, and a specificsolvent. As a result of these studies, the inventors of the presentinvention surprisingly discovered that a mesophase dope can be preparedfrom a cellulose derivative material dissolved in a solvent consistingof an aqueous solution of an inorganic acid, and the resultant dope isextremely stable in a wide range of concentration of the cellulosederivative material and in a wide range of the concentration of theinorganic acid in the dope.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a mesophase dopecontaining a cellulose derivative and an inorganic acid, which dope iscapable of exhibiting a stable mesophase property even in the case whereno fluid dynamic stress is applied thereto.

Another object of the present invention is to provide a mesophase dopecontaining a cellulose derivative and an inorganic acid, which dope isuseful for producing new type of filaments and/or films having a newtype of structure and excellent mechanical properties.

The above-mentioned objects can be attained by the mesophase dope of thepresent invention which comprises at least 10% by weight of at least onecellulose derivative contained in an aqueous solution of at least 5% byweights of at least one inorganic acid, said dope exhibiting a mesophaseproperty even in the case where no fluid dynamic stress is appliedthereto.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing relationships between the viscosities ofmesophase dopes containing (A) a cyanoethylcelluose (CyEC) having adegree of polymerization (DP) of 320 and a degree of substitution (DS)of 2.6, and a 73.5% nitric acid aqueous solution; (B) a methylcellulose(MC) having a DP of 750 and a DS of 1.8, and an 83% phosphoric acidaqueous solution, and; (C) a cellulose acetate (CA) having a DP of 250and a DS of 2.57, and a 65% nitric acid aqueous solution; andconcentrations of (A) (B) MC and (C) CA, respectively.

FIG. 2 is a graph showing a relationship between a percent of visibleray transmittance of a mesophase dope containing a carboxyethylcellulose(CEC) and nitric acid, and the concentration of CEC in the dope.

FIG. 3 is a polarized microscopic photograph showing a side view of afilament produced from a mesophase dope containing methylcellulose (MC)and phosphoric acid, as described in Example 1, in a magnification of520.

FIG. 4 is a polarized microscopic photograph showing a side view of afilm produced from a mesophase dope containing carboxyethylcellulose(CEC) and nitric acid, as described in Example 4, in a magnification of300. The arrow placed at the left of the photograph indicates thedirection of a spreading procedure applied to the mesophase dope forforming the film.

DETAILED DESCRIPTION OF THE INVENTION

In the mesophase dope of the present invention, the cellulose derivativeis preferably selected from the group consisting of cellulose ethers andcellulose esters. This is because: the cellulose ethers and estershaving a wide range of degree of substitution are soluble in the aqueoussolutions of the inorganic acids; the preparation of the celluloseethers and esters is easy; the degree of substitution and/or the degreeof polymerization of the cellulose ethers and esters can be adjusted todesired values in a strong acid solution, and; it is possible to producevarious shaped articles which exhibit different properties than those ofthe starting cellulose ethers or esters.

The cellulose ether usable for the present invention may be selectedfrom the group consisting of methylcellulose (MC), ethylcellulose (EC),cyanoethylcellulose (CyEC), carbamoylethylcellulose (CmEC),carboxyethylcellulose (CEC), cyanoethylcarbamoylethylcellulose(CyEC-CmEC), cyanoethylcarboxyethylcellulose (CyEC-CEC),carboxyethylcarbamoylethylcellulose (CEC-CmEC), hydroxyethylcellulose(HEC), ethylhydroxyethylcellulose (EHEC), hydroxypropylcellulose (HPC),hydroxypropylmethylcellulose (HPMC) carboxymethylcellulose (CMC),acetoxymethylcellulose (AMC) and acetoxymethylcellulose acetate (AMCA),and possible salts, for example, possible sodium salts, of theabove-mentioned cellulose ether compounds.

The cellulose ester usable for the present invention is preferablycellulose acetate.

The above-mentioned cellulose ethers and esters can be dissolved, in thestate of a molecular dispersion, in the aqueous solution of theinorganic acid.

Each of or a mixture of two or more of MC, CyEC, CEC, CyEC-CEC,CyEC-CmEC, CEC-CmEC, AMC, AMCA and CA is preferably used as a cellulosederivative for the present invention.

The high solubility of the cellulose derivative in the aqueous solutionof the inorganic acid is important for the formation of a mesophasedope.

This is because, it is necessary that the cellulose derivative bedissolved in a concentration of at least 10% by weight in the inorganicacid aqueous solution.

Generally, in a specific type of cellulose derivatives having a specificdegree of substitution, an increase in degree of polymerization (DP)causes a concentration of the cellulose derivative necessary for forminga mesophase dope in a specific inorganic acid aqueous solution todecrease. Usually, the degree of polymerization of the cellulosederivative usable for the present invention is not limited to a specialvalue. However, when the mesophase dope is used for the production ofshaped articles, it is preferable that the degree of polymerization ofthe cellulose derivative be 100 or more.

In the mesophase dope of the present invention, since the solventconsists of the aqueous solution of the inorganic acid, it is possibleto produce a stable mesophase dope even in the case where the degree ofsubstitution (DS) of the cellulose derivative is small, for example,less than 1.0 (DS<1). This feature of the mesophase dope of the presentinvention cannot be found in the conventional mesophase dopes, asdescribed in the above-mentioned Japanese patent application EarlyPublication No. 53-96230 (1978).

The solubility of the cellulose derivative in the inorganic acid aqueoussolution is variable depending upon the type of substituent and thedegree of substitution of the cellulose derivative. For example, CyECand CEC can form a mesophase dope in the inorganic acid aqueous solutionin the entire range of the degree of substitution, that is, satisfyingthe relation O<DS≦3.0, HPC and HEC exhibit the same mesophasedope-forming property as that of CyEC and CEC. However, in the cases ofEC and MC, the degree of substitution of more that 2.3 results in adecreased solubility thereof in the inorganic acid aqueous solution.Therefore, it is preferable that EC and MC have a degree of substitutionof 2.3 or less. Also, in the cases of CA, AMCA and AMC, the degree ofsubstitution thereof preferably satisfies the relation: O<DS≦2.7.

The inorganic acid usable for the mesophase dope of the presentinvention may be selected from the group consisting of hydrochloricacid, nitric acid, sulfuric acid, phosphoric acid, metaphosphoric acid,pyrophosphoric acid, hypophosphoric acid, sulfurous acid, fluorosulfuricacid, chlorosulfuric acid, chloric acid, hypochloric acid, chlorousacid, perchloric acid, bromic acid, perbromic acid, hypobromous acid,hydrofluoric acid, thiocyanic acid and thiosulfuric acid.

The above-mentioned inorganic acids may be used alone or in a mixture oftwo or more thereof. In practical use, at least one inorganic acid isdissolved in a concentration of at least 5% by weight in water. Theconcentration of the inorganic acid in the aqueous solution is variabledepending upon the types of the inorganic acid per se and the cellulosederivative to be dissolved. For example, in the case of MC having a DSof 2.3 or less, it is preferable that 12 to 35% by weight of MC bedissolved in an aqueous solution of phosphoric acid in a concentrationof 30% by weight or more, or nitric acid in a concentration of 50% byweight or more. In the case of CyEC having a DS of more than zero butnot exceeding 3.0, it is preferable that 20 to 45% by weight of CyEC bedissolved in an aqueous solution of nitric acid in a concentration of50% by weight or more. Also, in the case of CA having a DS of 2.7 orless, it is preferable that 20 to 38% by weight of CA be dissolved in anaqueous solution of nitric acid or sulfuric acid in a concentration of22% by weight or more. Furthermore, in the case of CA having a DS of0.35, it is preferable to use an aqueous solution of nitric acid in aconcentration of from 5 to 75% by weight.

If it is desired to control the hydrolysis of the cellulose derivativeor to prevent the decomposition of the cellulose derivative in theinorganic acid aqueous solution, the inorganic acid may be heatpretreated or the atmosphere in which the mesophase dope is prepared,may consist of nitrogen gas.

Generally speaking, in a combination of a specific cellulose derivativewith a specific inorganic acid, a decrease in the concentration of theinorganic acid in the aqueous solution results in a increase in theconcentration of the cellulose derivative necessary for forming amesophase dope.

The minimum concentration of a specific inorganic acid necessary forforming a mesophase dope of a specific cellulose derivative is variabledepending upon the types of the inorganic acid and the cellulosederivative used. For example, in the case of MC having a DS of 1.8 and aDP of 140, the minimum concentrations of hydrochloric acid and nitricacid necessary for forming a mesophase dope are 20% and 5% by weight,respectively.

Generally, in the mixture of an inorganic acid with water, the state ofthe inorganic acid per se is variable in response to the composition ofthe mixture. That is, the inorganic acid in the aqueous solution is notalways dissociated by water into a limiting state. This feature of theinorganic acid aqueous solution is different from that of mixtures of aconventional organic acid with water. Also, this feature is an importantfactor for forming a mesophase dope of the cellulose derivative.

In the mesophase dope of the present invention, since the aqueoussolution of the inorganic acid is used as a solvent for the cellulosederivative, it is possible to alter the viscosity of the dope to adesired value without changing the mesophase property of the dope. Forexample, in a mesophase dope of methylcellulose (MC) having a degree ofpolymerization (DP) of 650 and a degree of substitution (DS) of 1.8, anddissolved in an 85% sulfuric acid aqueous solution, a decrease in theviscosity of the dope to a value corresponding to 2/3 of the originalviscosity thereof, does not cause any change in the mesophase propertyof the dope usually, the hight viscosity of the mesophase dope causesdefoaming, extruding and spreading procedures for the dope to bedifficult, and a large amount of energy to be consumed for carrying outthe above-mentioned procedures. The above-mentioned disadvantages due tothe high viscosity can be prevented by reducing the viscosity of thedope without changing the mesophase property of the dope.

For example, a fresh mesophase dope produced from 40% by weight ofmethylcellulose and an 85% phosphoric acid aqueous solution exhibited avery high viscosity of about 3500 poises at a temperature of 25° C.Therefore one day or more was necessary for completely defoaming thefresh dope at a temperature of 0° C. Also, it was difficult to spreadthe fresh dope to form a film. However, when the viscosity of the dopewas reduced to 2200 poises at a temperature of 0° C. the heat-treateddope was easily spread to form a film.

In another example, even in the case where the viscosity of a mesophasedope containing 40% by weight of a cellulose acetate having a DP of 300and a DS of 2.45, and a 65% nitric acid aqueous solution, is reduced toa value corresponding to 1/2 of the original viscosity of the dope, byheat-treating it, at a temperature of 45° C., for 30 minutes, theheat-treated dope exhibited the same mesophase property as that of thenon-treated dope.

Also, it is possible to alter the degree of substitution of thecellulose derivative in the mesophase dope of the present invention byheat-treating the dope. The alteration in the degree of substitutioncauses the solubility of the cellulose derivative to be changed. Forexample, a mesophase dope containing an acetone-soluble celluloseacetate and a 65% nitric acid aqueous solution can be converted intoanother mesophase dope which is resistant to organic solvents and whichcan be used for producing a shaped article having a different structurefrom that produced from the non-converted dope.

The mesophase property of the dope can be determined by various methods.Almost all of the mesophase dopes of the present invention exhibit aninterfence color or a pearl color. Therefore, it is easy to recognizethe mesophase property of the dope of the present invention with thenaked eye. Otherwise, the mesophase property of the dope of the presentinvention can be recognized from the fact that a bright field of view isfound by observing dope placed between a glass plate and a cover glassplate, through an orthogonal Nicol's prism of a polarized microscope,even in the case where no shearing force is applied to the dope.

A range of the concentration of the cellulose derivative in which thedope can exhibit a mesophase property, can be determined from arelationship between the viscosity of the dope and the concentration ofthe cellulose derivative in the dope. Generally, in an isotropic dope ofa cellulose derivative, the molecular chains of the cellulose derivativeare entangled with each other. The viscosity of the isotropic dopeincreases with the increase in the concentration of the cellulosederivative in the dope. However, in the specific range of theconcentration of the cellulose derivative in which the dope exhibits amesophase property, the molecular chains of the cellulose derivativesare orientated in a specific arrangement, and therefore, the degree ofentanglement of the molecular chain decreases. This phenomenon causesthe viscosity of the dope to significantly decrease.

FIG. 1 shows relationships between the viscosities of dopes containing:(A) a cyanoethylcelulose (CyEC) having a degree of polymerization (DP)of 320 and a degree of substitution (DS) of 2.6, and a 73.5% nitric acidaqueous solution; (B) a methylcellulose (MC) having a DP of 750 and a DSof 1.8, and an 83% phosphoric acid aqueous solution, and; (C) acellulose acetate (CA) having a DP of 250 and a DS of 2.57, and a 65%nitric acid aqueous solution; and the concentrations of CyEC in the dope(A) MC in the dope (B) and CA in the dope (C), respectively. Theviscosities of the dopes were determined at a shearing velocity of 20sec.⁻¹, at temperature of 5° C., by using a cone plate-type rotationviscometer. In FIG. 1, the dope (A) exhibits an isotropic property inregion X and an anisotropic property in region Y. FIG. 1 shows that ineach of the dopes (A), (B) and (C), the viscosity of the dope remarkablydecreases in a range of the concentration of the cellulose derivative inwhich the mesophase phase is separated from the dope, and then, theviscosity increases in a range of the concentration of the cellulosederivative in which the separation of the mesophase phase is completed.

FIG. 2 shows a relationship between a percent of transmittance ofvisible rays through a dope containing a carboxyethylcellulose (CEC)having a DP of 290 and a DS of 2.2, and a 60% nitric acid aqueoussolution, and a concentration of CEC in the dope. The percent oftransmittance of the visible rays was determined by using a light havinga wave length of 720 mm at a temperature of 25° C. In FIG. 2, the dopeexhibits an isotropic property in regions X₁ and X₂, and an anisotropicproperty in a region Y.

Based on FIG. 2, it is considered that, since there is a relationshipbetween the percent of transmittance of the visible rays for the dopeand the birefringence coefficient of the dope, and the birefringencecoefficient of the dope depends upon the arrangement of the molecularchains of the cellulose derivative in the dope, the percent oftransmittance of the dope becomes maximum in a specific range of theconcentration of the cellulose material in the dope in which the dopeexhibits a mesophase property, due to the specific orientation of themolecular chains of the cellulose derivatives therein. The theoreticalreason for the above-mentioned phenomenon has not yet been clarified.

The mesophase dope of the present invention does exhibit a stablemesophase property without applying a fluid dynamic stress thereto. Forexample, dopes of cyanoethylcellulose in a nitric acid aqueous solution,methylcellulose in a phosphoric acid aqueous solution,carboxyethylcellulose in a nitric acid aqueous solution, methylcellulosein a nitric acid aqueous solution and cyanoethylcellulose in aphosphoric acid aqueous solution, can exhibit the mesophase propertyover a period of from several days to several weeks from the preparationthereof, at a temperature of from 0° C. to room temperature. Comparedwith the above-mentioned dopes of the present invention, almost all ofthe conventional dopes containing, for example, a cellulose ether in anorganic solvent, and the aqueous dopes as described in Japanese patentapplication Laid-open (Kokai) No. 55-96230, except for the dopes ofethylcellulose in a methyl alcohol-methylchloride type solvent, exhibita mesophase property which is relaxed within several minutes or severalseconds from the preparation thereof. Also, almost all of theabove-mentioned conventional cellulose ether dopes must be stimulted bya fluid dynamic stress in order to exhibit the mesophase property.Accordingly, the mesophase dopes of the present invention can bedefinitely distinguished from the conventional mesophase dopes.

The mesophase dope of the present invention can be prepared by mixing aspecific cellulose derivative with an inorganic acid aqueous solutionand, then, by stirring the mixture at room temperature, or while coolingor heating it.

In the preparation of the mesophase dope of the present invention, thepossibility of formation of undesirable gel is extremely low. Therefore,the mesophase dope useful for producing various shaped articles can beeasily obtained within a short time. For example, in the case ofpreparation of a mesophase dope from cyanoethylcellulose and a 65%nitric acid aqueous solution, the preparation can be completed within 3to 5 hours without formation of gel. However, in the case where dimethylformamide is used as a solvent for the cyanoethylcellulose, in place ofthe 65% nitric acid aqueous solution, a large amount of gel is producedin the mixture, and therefore, it is extremely difficult to obtain amesophase dope useful for the production of shaped articles. Generally,if the mesophase dope containing a high concentration of the cellulosederivative and, therefore, having a high viscosity, contains the gel, itis very difficult to remove the gel from the dope by means offiltration. However, the mesophase dope of the present inventioncontains substantially no gel. Therefore, the mesophase dope of thepresent invention can be subjected to the production of shaped articles,without the filtration procedure. This feature of the present inventionis very advantageous in industry.

In the mesophase dope of the present invention, it is possible todepolymerize the cellulose derivative at a proper temperature to convertit to a modified mesophase dope having a desired viscosity. In thiscase, generally, the modified mesophase dope is further converted into auniform dope having no mesophase property by elevating the temperatureof the dope. However, by lowering the temperature of the uniform dope,the mesophase dope is reversibly reproduced from the uniform dope.

The mesophase dope of the present invention is advantageous in thefollowing matters.

1. The solvent consisting of an inorganic acid aqueous solution ischeap. Therefore, the cost of the production of the mesophase dope islow.

2. By hydrolyzing the cellulose derivative in the dope, the viscosity ofthe dope can be adjusted to a desired value while the mesophase propertyof the dope is maintained. The mesophase dope having a desired viscosityis advantageously utilized for the production of various shapedarticles.

3. The relaxation time of the mesophase dope is very long so that aslong as the dope is stored at a proper temperature, the mesophaseproperty can usually be stably maintained for from several days toseveral weeks.

4. Various types of mesophase dopes can be produced from various typesof cellulose derivatives having a wide range of degree of substitution.Therefore, various new types of shaped articles having various differentproperties can be obtained from the mesophase dopes.

5. Basically, the mesophase dope can be produced by using a singlesolvent. Therefore, the preparation procedure of the mesophase dope isvery easy and the solvent can be easily recovered.

6. When the mesophase dope is converted into a shaped article, forexample, a filament or film, the amount of the solvent retained in theshaped article is much smaller than that when an organic solvent isused. Therefore, the purity and whiteness of the resultant shapedarticle are better than those when the organic solvent is used.

The mesophase dope of the present invention can be used for theproduction of a film or filaments having a new structure. In the case ofthe production of a filament yarn consisting of a cellulose derivativeand having an excellent mechanical strength from the mesophase dope, itis preferable that an air-jet-wet spinning process be used. In theprocess, the filaments extruded through a spinneret located in an airatmosphere, are introduced vertically into a coagulation bath. Aftermoving vertically, the coagulated filaments further move along pinslocated in the coagulation bath. The coagulated filaments are removedfrom the coagulation bath and, finally, wound on a bobbin.

The coagulation bath also can be used for coagulating a film or anothershaped article formed from the mesophase dope of the present invention.The temperature of the coagulation bath is preferably in a range of from0 to 15° C. The coagulation bath usually consists of at least one memberselected from methyl alcohol, water, acetone, ether and mixtures thereofwith an inorganic acid and/or inorganic salt. The composition of thecoagulation bath is determined in response to the type of the cellulosederivative and the type of the inorganic acid in the aqueous solution.The above-mentioned coagulation bath is effective for extracting theinorganic acid from the mesophase dope. In order to completely removethe inorganic acid from the shaped article, it is effective to immersethe shaped article in the coagulation bath for a long period of time,for example, one day and night.

The specific examples presented below will serve to more fully elaboratehow the present invention is practiced. However, it should be understoodthat the examples are only illustrative and in no way limit the scope ofthe present invention.

EXAMPLE 1

A dope was prepared by dissolving 30 parts by weight of methylcellulose(MC) having a degree of polymerization (DP) of 220 and a degree ofsubstitution (DS) of 1.8 in 70 parts by weight of a 83% phosphoric acidaqueous solution at a temperature of 15° C. The resultant dope exhibiteda mesophase property. The dope was degased, and then, extruded into acoagulation bath through a single spinning hole having a diameter of0.12 mm. The spinning hole was located 0.5 cm above the level surface ofthe coagulation bath. The extruded monofilamentary stream of the dopewas introduced into the coagulation bath which consisted of acetonecontaining 5% by weight of an 85% phosphoric acid aqueous solution. Thecoagulated MC monofilament was removed from the coagulating bath andwound up on a bobbin at a winding speed of 20 m/min. The filament had adenier of 25. The filament on the bobbin was immersed in a mixture of 1part by weight of ether and 3 parts by weight of methyl alcohol for onehour, washed with methyl alcohol and, finally, air dried.

The resultant MC monofilament was subjected to polarized microscopicobservation. FIG. 3 shows a polarized microscopic side view of aperipheral surface of the MC monofilament. In FIG. 3, a number ofgrooves and protuberances are formed on the peripheral surface of thefilament. The grooves and protuberances extend at about a right angle tothe longitudinal axis of the filament. This type of grooves andportuberances are never found on conventional methylcellulose filaments.The MC monofilament had the following properties.

Tensile strength: 3.5 g/d

Ultimate elongation: 5˜6%

Initial modulus: 50˜80 g/d

The same procedures as those described above were applied to each of thecombinations of: 55% by weight of a MC having a DP of 95 and a DS of 1.8with 45% by weight of a 35% hydrochloric acid aqueous solution; 25% byweight of a MC having a DP of 340 and a DS of 1.8 with 75% by weight ofa 65% nitric acid aqueous solution; 35% by weight of a MC having a DP of580 and a DS of 1.8 with 65% by weight of a 72% sulfuric acid aqueoussolution; 30% by weight of a MC having a DP of 750 and a DS of 1.8 with70% by weight of a 60% perchloric acid aqueous solution; 25% by weightof a MC having a DP of 220 and a DS of 1.8 with 75% by weight of a 83%phosphoric acid aqueous solution, and; 15% by weight of a MC having a DPof 750 and a DS of 1.8 with 85% by weight of a 83% phosphoric acidaqueous solution.

All of the resultant dopes exhibited a mesophase property and could beconverted into monofilaments similar to the above-mentionedmonofilament, without difficulity.

EXAMPLE 2 AND COMPARATIVE EXAMPLE 1

In Example 2, a mesophase dope which is useful for producing a filamenthaving an excellent mechanical strength and a high degree oforientation, was produced by using a cyanoethylcellulose (DS=2.89,DP=390) and an inorganic acid aqueous solution, and then, the dope wasconverted into a multifilament yarn. In Comparative Example 1, anorganic solvent was used in instead of the inorganic acid aqueoussolution, in order to compare the effect of the latter with the effectof the former.

In Example 2, a mixture of 300 g of a 73.5% nitric acid aqueous solutionand 200 g of the above-mentioned cyanoethylcellulose was stirred in aone liter dissolving vessel, at room temperature, for four hour. Auniform mesophase dope containing no gel was easily obtained. Themesophase dope was allowed to stand at a temperature of 0° C., for oneday, and then, degased under a reduced pressure. The degased dope wasextruded into a coagulation bath through a spinneret having 50 holes,each having a diameter of 0.07 mm and located 0.5 cm above the levelsurface of the coagulation bath, at a extruding rate of 2.5 cc/min. Thecoagulation bath consisted of a 20% nitric acid aqueous solution and hada temperature of -5° C. The coagulated cyanoethylcellulose filamentswere wound up on a bobbin at a speed of 60 m/min. The filaments on thebobbin were immersed in water for one day to remove the nitric acid and,finally, air dried. The properties of the dried filaments are indicatedin Table 2.

In Japanese patent application Laid-open No. 52-96230-(1977),dimethylformamide (DMF) are used as a solvent for cyanoethylcellulose toprovide a mesophase dope. Accordingly, in Comparative Example 1, 35% byweight of the same cyanoethylcellulose as that mentioned in Example 2were mixed with 65% by weight of dimethylformamide at a temperature of25° C, and the mixture was stirred. A slurry was obtained. In order toconvert the slurry into a mesophase dope, it was necessary to continuethe stirring procedure for a long period of 15 to 18 hours. Theresultant dope was in the state of a gel and exhibited a very poorfiber-forming property. Therefore, it was impossible to conduct aspinning procedure by using the dope.

Separately, a dope of 25% by weight of the cyanoethylcellulose 75% byweight of dimethylformamide was prepared. The dope exhibited nomesophase property. The dope was extruded in the same manner as thatmentioned in Example 2 into a coagulating bath consisting of 20% byweight of methyl alcohol and 80% by weight of water. The resultantfilaments on a bobbin were immersed in a mixture of 10% by weight ofmethyl alcohol and 90% by weight of water, at a room temperature, forone day, and then, air dried. The properties of the resultantcomparative filaments are indicated in Table 2.

                  TABLE 2                                                         ______________________________________                                                         Tensile  Ultimate                                                                              Initial                                                      strength elongation                                                                            modulus                                                                              White-                               Example No.                                                                            Denier  (g/d)    (%)     (g/d)  ness                                 ______________________________________                                        Example 2                                                                              103     5.6      4.0     137    86                                   Comparative                                                                            81      2.9      8.6     42.3   65                                   Example 1                                                                     ______________________________________                                    

The whiteness of the filaments was represented by the reflectivity ofthe filaments when a light having a wave length of 400 μm was applied tothe filaments by using a colorimeter. The larger the amount of thesolvent retained in the filaments, the lower the whiteness of thefilaments.

From Table 2, it is clear that the filaments of Example 2 exhibited ahigher whiteness, that is, a higher degree of purity, than that ofComparative Example 1. Also, the filaments of Example 1 had a highertensile strength and initial modulus than those of Comparative Example1.

Furthermore, it is clear that it is very difficult to obtain, by usingan organic solvent, a mesophase dope of a cellulose derivative, which isusable for producing a shaped article, for example, filaments, becauseof the formation of undesirable gel in the dope.

EXAMPLE 3

In this example, 16 types of dopes were prepared at a temperature of 0°C. from various types of non-fractioned cellulose acetates having adegree of polymerization of from 250 to 300 and various types ofinorganic acid, in the same manner as that described in Example 1. Thecompositions of the dopes are indicated in Table 3.

                  TABLE 3                                                         ______________________________________                                        Inorganic acid solution                                                                            Cellulose acetate                                        No. of           Concentration     Concentration                              dope  Type       (wt %)      DS    (wt %)                                     ______________________________________                                         (1)  Nitric     65          2.57  35                                          (2)  acid       30          1.98  40                                          (3)             30          1.22  45                                          (4)              5          0.35  44                                          (5)  Sulfuric   96          2.57  30                                          (6)  acid       60          1.98  40                                          (7)             20          1.22  50                                          (8)             20          0.35  40                                          (9)  Phosphoric 83          2.57  30                                         (10)  acid       83          1.98  35                                         (11)             30          1.22  40                                         (12)             30          0.35  45                                         (13)  Perchloric 60          2.57  40                                         (14)  acid       60          1.98  35                                         (15)             60          1.22  40                                         (16)             60          0.35  45                                         ______________________________________                                    

All of the resultant dopes exhibited mesophase properties and could beconverted to monofilaments similar to that described in Example 1, inthe same manner as that mentioned in Example 1.

EXAMPLE 4

In this example, ten types of dope, each having a composition asindicated in Table 4, were prepared. The cellulose diacetate used had aDS of 2.56 and a DP as indicated in Table 4.

                  TABLE 4                                                         ______________________________________                                                         Cellulose diacetate                                          No. of                          Concentration                                 dope   Inorganic acid solution                                                                       DP       (wt %)                                        ______________________________________                                        17     65% nitric acid about 600                                                                              10                                            18                     about 250                                                                              30                                            19     60% Perchloric acid                                                                           about 450                                                                              18                                            20                     about 100                                                                              32                                            21     83% phosphoric acid                                                                           about 300                                                                              25                                            22                     about 100                                                                              34                                            23     60% sulfuric acid                                                                             about 600                                                                              18                                            24                     about 450                                                                              25                                            25                     about 300                                                                              30                                            26                     about 250                                                                              30                                            ______________________________________                                    

All of the prepared dopes exhibited mesophase properties and could beconverted into monofilaments similar to that described in Example 1, inthe same manner as that described in Example 1.

EXAMPLE 5

In this example, eight types of dopes, each having a composition asindicated in Table 5, were prepared in the same manner as that describedin Example 1. The cyanoethylenecellulose (CyEC) used had a DS of 0.3 anda DP of 620, and the carboxyethylcellulose (CEC) used had a DS of 0.8and a DP of 550.

                  TABLE 5                                                         ______________________________________                                                          Cellulose derivative                                        No. of                           Concentration                                dope   Inorganic acid solution                                                                        Type     (wt %)                                       ______________________________________                                        27     85% phosphoric acid                                                                            CyEC     20                                           28     85% phosphoric acid                                                                            CEC      20                                           29     60% nitric acid  CyEC     25                                           30                      CEC      20                                           31     65% sulfuric acid                                                                              CyEC     30                                           32                      CEC      30                                           33     30% hydrochloric acid                                                                          CyEC     40                                           34                      CEC      50                                           ______________________________________                                    

All of the resultant dopes exhibited a mesophase property. The mesophasedope No. 30 was spread on an upper surface of a horizontal glass plateto form a film of the dope. The dope film spread on the glass plate wasimmersed in a coagulation bath consisting of methyl alcohol at atemperature of 10° C. The coagulated CEC film was washed with ethylalcohol and, finally, air dried. A transparent thin film having athickness of 24 microns was obtained. The film was subjected topolarized microscopic observation. The photograph of the surface view ofthe film is indicated in FIG. 4. In view of FIG. 4 the film ischaracterized by a stripe pattern formed on the surface thereof, thestripes extend at about a right angle to the direction in which the dopewas spread on the glass plate.

EXAMPLE 6 AND COMPARATIVE EXAMPLES 2 AND 3

In Example 6, a mesophase dope was prepared from a combination of awater-soluble cellulose monoacetate having a degree of substitution of0.35 and a 60% perchloric acid aqueous solution, and a new structure offilaments was prepared from the mesophase dope.

40% by weight of the above-mentioned cellulose monoacetate weredissolved in 60% by weight of the 60% perchloric acid aqueous solution Auniform mesophase dope was obtained.

The dope was subjected to the same spinning process as described inExample 1, except that the coagulating bath consisted of methyl alcohol.The coagulated filaments were satisfactorily washed with a mixture of 40parts by weight of methyl alcohol and 60 parts by weight of ethyl ether,and finally, air dried. The resultant cellulose monoacetate filamentseach had a number of grooves formed on the peripheral surface thereofsimilar to those formed on the methylcellulose filaments of Example 1.

The filaments had the following properties.

Tensile strength: 4.1 g/d

Ultimate elongation: 4%

Initial modulus: 92 g/d

In Comparative Example 2, the same procedures as those described inExample 6 were carried out, except that water was used in place of the60% perchloric acid aqueous solution. The resultant filaments had nogrooves formed on the peripheral surfaces thereof. The properties of thecomparative filaments were as follows.

Tensile strength: 1.3 g/d

Ultimate elongation: 6%

Initial modulus: 17 g/d

In Comparative Example 3, the same procedures as those mentioned inExample 6 were carried out, except that the 60% perchloric acid aqueoussolution was replaced by an organic solvent consisting oftrifluoroacetic acid alone. The resultant dope exhibited no mesophaseproperty. When the concentration of the cellulose monoacetate wasincreased to 60% by weight or more, the resultant dope could exhibit themesophase property only after stirring the dope over a long period of 15to 20 hours. However, the resultant dope contained a large amount ofcellulose monoacetate not dissolved in the organic solvent. Therefore,the dope could not be used for the spinning process.

EXAMPLE 7

In this example, six different types of dopes, each having a compositionas indicated in Table 6, were prepared by using a methylcellulose havinga DS of 1.8 and a DP of 140, in the same manner as that described inExample 1.

                                      TABLE 6                                     __________________________________________________________________________                 No. of dope                                                                   35     36   37  38   39    40                                    __________________________________________________________________________    Type of inorganic acid                                                                     Hydrochloric                                                                         Sulfuric                                                                           Nitric                                                                            Phospho-                                                                           Pyrophos-                                                                           Perchloric                                         acid   acid acid                                                                              ric  phoric                                                                              acid                                                               acid acid                                        Concentration of inorganic                                                                 25     35   10  35   40    20                                    acid (% by weight)                                                            Concentration of MC                                                                        50     50   50  40   40    55                                    (% by weight)                                                                 __________________________________________________________________________

All of the above-prepared dopes exhibited a mesophase property and couldbe converted into methylcellulose filaments similar to those describedin Example 1.

EXAMPLE 8

In this example, four different types of dopes, each having acomposition as indicated in Table 7, were prepared. The resultant dopesexhibited a mesophase property and had a viscosity as indicated in Table7, at a temperature of 25° C.

Each of the resultant dopes were subjected to a heat treatment with hotwater, at a temperature of 60° C., for 10, 30 or 60 minutes, andthereafter, cooled to a temperature of 25° C. The heat-treated dopes hada viscosity as indicated in Table 7. The cooled dopes, which had beenheat-treated for 30 minutes or less, exhibited the mesophase property,and could be converted into films in the same manner as that describedin Example 5. However, the cooled dopes which had been heat treated at60° C. for 60 minutes, exhibited no mesophase property.

When the non-heat treated dope No. 41 could be degased under a reducedpressure of 20 mmHg, at a temperature of 0° C., along time of 12 to 16hours was needed to complete the degassing procedure. However, thedegassing procedure for the dope No. 41, which had been heat treated at60° C. for 30 minutes, could be completed within a short time of 4 to 6hours, under the same conditions as those mentioned above.

                                      TABLE 7                                     __________________________________________________________________________                              Viscosity of dope (poise)                           Cellulose derivative       Non-                                               No. of  concentration                                                                        Inorganic  heat-                                                                             Heat treated at 60° C.                   dope                                                                              Type                                                                              (wt %) acid solution                                                                            treated                                                                           10 min                                                                            30 min                                                                            60 min                                  __________________________________________________________________________    41  CyEC                                                                              25     81% phosphoric acid                                                                      2300                                                                              1600                                                                              1100                                                                              900                                     42  EC  40     mixture*.sup.1                                                                           1100                                                                               700                                                                              500 400                                     43  MC  40     60% perchloric acid                                                                       900                                                                               500                                                                              400 300                                     44  CEC 30     63% nitric acid                                                                          1800                                                                              1100                                                                              800 350                                     __________________________________________________________________________     Note:                                                                         *.sup.1 Mixture of 4 parts by volume of a 35% hydrochloric acid aqueous       solution and 1 part by volume of a 65% nitric acid aqueous soluture.          CyEC: DP = 350, DS = 2.6                                                      EC: DP = 240, DS = 1.4                                                        MC: DP = 180, DS = 1.8                                                        CEC: DP = 340, DS = 0.3                                                  

EXAMPLE 9

A dope was prepared by stirring a mixture of 325 g of a 60% nitric acidaqueous solution and 175 g of a cellulose acetate having a DP of 250 anda DS of 2.57, in a one liter reaction vessel at a room temperature. Thedope was aged at a temperature of 50° C. for 30 minutes and, thereafter,allowed to stand at a temperature of 0° C. for one day. A mesophase dopewas obtained.

The dope was degased and, thereafter, extruded through a spinnerethaving 50 spinning holes, having a diameter of 0.08 mm, into acoagulation bath. The spinning holes were located 0.5 cm above the levelsurface of the coagulating bath which consisted of an aqueous solutionof 15% by weight of nitric acid and 20% by weight of sodium nitrate andhad a temperature of from 0° to 4° C. The coagulated filaments werewound up from the coagulating bath onto a bobbin at a winding speed of60 m/min. The filaments on the bobbin were washed with water to removethe nitric acid and the coagulating liquid and, then, air dried. Theresultant filaments had the following properties.

Denier: 142/50 filaments

Tensile strength: 4.4 g/d

Ultimate elongation: 8.5%

Initial modulus: 73 g/d

The filaments were insoluble in acetone and mixtures of methylenechloride and methyl alcohol which were capable of dissolving thecellulose diacetate used in this example as a starting material.

EXAMPLE 10

In this example, various types of mesophase dopes, each having acomposition as indicated in Table 8, were prepared in the same manner asthat described in Example 1.

                  TABLE 8                                                         ______________________________________                                        Cellulose derivative                                                                              Con-                                                      No.                 cen-                                                      of                  tration                                                   dope Type           (wt %)  Inorganic acid solution                           ______________________________________                                        45   HEC*.sup.1     40      35% hydrochloric acid                             46   (250 cps,      40      72% sulfuric acid                                 47   M.S.*.sup.2 = 1.8)                                                                           45      60% perchloric acid                               48   EC*.sup.3      35      65% nitric acid                                   49   (DS = 0.6)     40      Mixture*.sup.4                                    50                  50      60% perchloric acid                               51   CYEC*.sup.5    45      30% hydrochloric acid                             52   (DP = 300,     45      20% hydrochloric acid                             53   DS = 2.5)      30      83% phosphoric acid                               54                  30      50% phosphoric acid                               55                  30      65% pyrophosphoric acid                           56   CYEC--CEC*.sup.6                                                                             40      72% nitric acid                                   57   (DS = 1.5 (average))                                                                         40      60% hypochlorous acid                             58                  37      40% sulforous acid                                59   HPC*.sup.7     40      5% nitric acid                                    60   (M.S. = 2.4)   40      12% hydrochloric acid                             61   CMC*.sup.8     27      73% nitric acid                                   62   (DS = 0.8)     30      72% sulfuric acid                                 ______________________________________                                         Note:                                                                         *.sup.1 hydroxyethylcellulose                                                 *.sup.2 molecular substitution                                                *.sup.3 ethylcellulose                                                        *.sup.4 mixture of 4 parts by volume of a 35% hydrochloric acid and 1 par     by volume of a 65% nitric acid                                                *.sup.5 cyanoethylcellulose                                                   *.sup.6 cyanoethylcellulosecarboxyethylcellulose copolymer                    *.sup.7 hydroxypropylcellulose                                                *.sup.8 carboxymethylcellulose                                           

EXAMPLE 11

In this example, five different types of mesophase dopes were prepared,each having a composition as indicated in Table 9, in the same manner asthat mentioned in Example 1.

                  TABLE 9                                                         ______________________________________                                                        Cellulose derivative                                                                             Concen-                                    No. of                             tration                                    dope  Inorganic acid solution                                                                       Type         (wt %)                                     ______________________________________                                        63    100% chlorosulfuric acid                                                                      CA(DS = 2.56)                                                                              40                                         64    78% thiosulfuric acid                                                                         HEC(DS = 0.8)                                                                              50                                         65    82% metaphosphoric acid                                                                       MC(DS = 1.8) 45                                         66    65% thiocyanic acid                                                                           CYEC(DS = 0.8)                                                                             40                                         67    50% bromic acid MC(DS = 0.8) 55                                         ______________________________________                                    

COMPARATIVE EXAMPLE 4

The same procedures as those mentioned in Example 2 were carried out,except that the CYEC was used in a concentration of 9.5% by weight. Theresultant dope exhibited no mesophase property. Also, the resultantfilaments had the following properties.

Denier: 45/50 filaments

Tensile strength: 2.2 g/d

Ultimate elongation: 15%

Initial modulus: 24 g/d

The degree of orientation of the molecular chains in the filaments waspoor.

COMPARATIVE EXAMPLE 5

The same procedures as those described in Example 1 were carried out,except that the 83% phosphoric acid aqueous solution was replaced bywater and the MC was used in a concentration of 30% by weight. Theresultant dope exhibited no mesophase property. The resultantmonofilament had the following properties.

Tensile strength: 1.2 g/d

Ultimate elongation: 10%

Initial modulus: 15 g/d

The filament had substantially no grooves and protuberance formed on theperipheral surface thereof.

We claim:
 1. A mesophase dope comprising at least 10% by weight of atleast one cellulose ester having a degree of substitution (DS) of lessthan 2.7 and being dissolved in an aqueous solution of at least 5% byweight of at least one inorganic acid, said dope exhibiting a mesophaseproperty even in the case where no fluid dynamic stress is appliedthereto.
 2. A mesophase dope as claimed in claim 1, wherein saidcellulose ester is selected from the group consisting of celluloseacetate and acetoxymethylcellulose acetate.
 3. A mesophase dope asclaimed in claim 1, wherein said inorganic acid is selected from thegroup consisting of hydrochloric acid, nitric acid, sulfuric acid,phosphoric acid, metaphosphoric acid, pyrophosphoric acid,hypophosphoric acid, sulfurous acid, fluorosulfuric acid, chlorosulfuricacid, chloric acid, hypochlorous acid, chlorous acid, perchloric acid,bromic acid, perbromic acid, hypobromous acid, hydrofluoric acid,thiocyanic acid, and thiosulfuric acid.
 4. A mesophase dope as claimedin claim 1, wherein said inorganic acid is selected from the groupconsisting of hydrochloric acid, nitric acid, sulfuric acid, phosphoricacid, perchloric acid, pyrophosphoric acid, chlorosulfuric acid,thiosulfuric acid, metaphosphoric acid, thiocyanic acid, and bromicacid.
 5. A mesophase dope as claimed in claim 1, wherein an aqueoussolution of nitric acid or sulfuric acid contains cellulose acetate.